Fired when a connection is made with either an add-on process or a content script.


  port // Port
) {...})

This API is also available as browser.runtime.onConnect.*.

Events have three functions:

Adds a listener to this event.
Stop listening to this event. The listener argument is the listener to remove.
Checks whether a listener is registered for this event. Returns true if it is listening, false otherwise.

addListener syntax



A callback function that will be called when this event occurs. The function will be passed the following arguments:

A runtime.Port object connecting the current script to the other context it is connecting to.

Browser compatibility

Chrome Edge Firefox Firefox for Android Opera
Basic support Yes No 45.0 48.0 33


This content script:

  • connects to the background script, and stores the Port in a variable myPort
  • listens for messages on myPort, and logs them
  • sends messages to the background script, using myPort, when the user clicks the document
// content-script.js

var myPort = chrome.runtime.connect({name:"port-from-cs"});
myPort.postMessage({greeting: "hello from content script"});

myPort.onMessage.addListener(function(m) {
  console.log("In content script, received message from background script: ");

document.body.addEventListener("click", function() {
  myPort.postMessage({greeting: "they clicked the page!"});

The corresponding background script:

  • listens for connection attempts from the content script
  • when it receives a connection attempt:
    • stores the port in a variable named portFromCS
    • sends the content script a message using the port
    • starts listening to messages received on the port, and logs them
  • sends messages to the content script, using portFromCS, when the user clicks the add-on's browser action
// background-script.js

var portFromCS;

function connected(p) {
  portFromCS = p;
  portFromCS.postMessage({greeting: "hi there content script!"});
  portFromCS.onMessage.addListener(function(m) {
    console.log("In background script, received message from content script")


chrome.browserAction.onClicked.addListener(function() {
  portFromCS.postMessage({greeting: "they clicked the button!"});


This API is based on Chromium's chrome.runtime API. This documentation is derived from runtime.json in the Chromium code.

Microsoft Edge compatibility data is supplied by Microsoft Corporation and is included here under the Creative Commons Attribution 3.0 United States License.

Document Tags and Contributors

 Contributors to this page: Makyen, chrisdavidmills, wbamberg, rolfedh
 Last updated by: Makyen,